Lab 14 - Selective and Differential Media Flashcards
what is biotyping?
To characterize a microbe based on its metabolic properties. This is determined by physical conditions like temperature, O2 concentration, etc.
why is biotyping useful?
it is useful in the classification of microbes and the identification of unknown microbes.
what are bacterial strains identified using biotypes called?
biovars
what are some questions we can answer using biotyping tests?
-Which components can the bacteria use as a source of energy (aka what is it eating)?
-What gases or temperatures are required for its growth?
-Which waste products do the bacteria make (acids, bases, etc)?
-Which specific substances inhibit the growth of the bacteria (antibiotics, salt, etc.)?
-Which proteins do the bacteria secrete while growing (what does it spit out)?
These tests/questions are based on the ability of the bacterial species to make what things?
These tests/questions are based on the ability of the bacterial species to make certain enzymes, transport proteins, outer membranes, or secreted proteins.
We are basically trying to figure out the enzymes and proteins, etc. present.
what are the two types of general growth media?
-Rich medium
-Minimal medium
what does a rich medium contain?
It contains rich sources of nutrients to support the growth of a broad range of microbes, for example, NA, TSA, etc.
We don’t know the exact components or quantities. (Undefined or complex medium)
do we know the exact components or quantities present in a rich medium?
no, we do not.
what is in a minimal medium?
It contains minimum nutrients to support the growth of microbes.
We know the exact quantity, amounts, and materials. (Defined medium).
do we know the exact components of quantities present in a minimal medium?
yes, we do.
A minimal medium can support the growth of what, and cannot support the growth of what?
A minimal medium:
-Supports the growth of phototrophs that DO NOT need growth factors.
-Cannot support the growth of auxotrophs that NEED growth factors. Ex: trp- mutant (which needs tryptophan) and his- mutant (needs histidine)
what is an Arginine Auxotroph?
It needs Arginine to grow.
Will growth occur in an Arginine Auxotroph in the following media:
-Minimal Media
-Minimal Media + Arginine
-Minimal Media + Lysin
Minimal Media: no growth
Minimal media + Arginine: yes, growth.
Minimal media + Lysine: no growth
what is select growth media?
A select growth media that can only allow the growth of certain types of microbes and can suppress the growth of other types.
Enterococcus isolation agar only allows growth of bacteria from what genus?
From the genus Enterococcus
When a medium selects “FOR” enterocci, what does that mean?
that means this bacteria CAN grow here
When a medium selects “AGAINST” a bacteria, what does that mean?
that means a bacteria CANNOT grow here
what is a routine medium?
not selective or differential
what is a differential growth medium?
this type of media allows the growth of 2 different types of bacteria, which appear different from each other helping in identification
what is an example of a differential growth medium?
tributyrin agar
what is a tryptic soy agar? what is the abbreviation?
TSA, contains carbohydrates, peptides, salts, ions, 0.5% NaCl, etc.
In TSA, what does a bacteria use first out of carbohydrates and amino acids?
The bacteria prefers and will use carbohydrates first and then amino acids as a source of energy.
what is a Mannitol Salt Agar? what is its abbreviation?
MSA, contains:
-Mannitol sugar: peptides, salts, and ions.
-7.5% NaCl
-Phenol red - pH indicator (neutral = pink; acidic = yellow, basic = red)
what is MSA used to distinguish between?
MSA is used to distinguish between common skin microflora bacterial species - Staphylococcus epidermis and the pathogenic species Staphylococcus aureus
what does the high NaCl concentration of MSA suppress?
the high NaCl concentration in MSA suppresses the growth of most skin microbes except Staphylococcus
In MSA, what does S. aureus ferment? What color does the medium turn into?
in MSA, S. aureus ferments mannitol to produce acids, which turn the medium yellow
Can S. epidermidis ferment mannitol in MSA? What does it use as a source of energy? What color does the medium turn into?
No, S. epidermidis cannot ferment mannitol in MSA. So it uses amino acids as a source of energy. During this process, amino acids are deaminated to produce ammonia, which is basic and turns the medium red.
is MSA selective or differential?
It is both, it is selective for halotolerant microbes. It is differential for mannitol fermenters and non-fermenters.
in MSA, what does the yellow color indicate?
It indicates the growth of S. aureus
in MSA, what does the pink/red color indicate?
it indicates the growth of S. epidermidis
what does Eosin Methylene Blue contain? What is its abbreviation?
EMB, it contains:
-Lactose and Sucrose sugars
-Peptides
-Salts, ions
-Eosin Y, Methylene blue
what is EMB selective for?
It is selective for Gram-negative bacteria as eosin Y and methylene blue inhibit the growth of Gram-positive bacteria
in EMB, if bacteria ferment lactose or sucrose, what do they produce?
they produce acids
in EMB, if there is less acid, what is shown and what does it mean? How about for more acid?
-Less acid: pink colonies - which are slow fermenters.
-More acid: purple/black/metallic green colonies - fast fermenters
in EMB, if bacteria use peptides, is there a color change in the colonies?
No, there is no color change, it would be clear.
RESULTS: In the TSA medium, what was present of the four bacteria?
-Pseudomonas aeruginosa: was present. It was a light green pigment and we saw general growth.
-Escherichia coli: was present.
-Staphylococcus aureus: was present. It was a yellowish growth.
-Staphylococcus epidermidis: was present.
RESULTS: In the MSA medium, what was present of the four bacteria?
-P. aeruginosa: was NOT present because it was not halotolerant.
-E. coli: was NOT present because it was not halotolerant.
-S. aureus: was present, yellowish growth.
-S. epidermidis: was present, pink growth (since it cannot ferment mannitol, it turns pink).
RESULTS: In the EMB medium, what was present of the four bacteria?
-P. aeruginosa: no growth
-E. coli: was present. Metallic green growth (fast fermenter).
-S. aureus: NOT present, but sometimes a little growth is seen.
-S. epidermidis: NOT present
RESULTS: what were the unknown bacteria, and how do we know what they were?
The two unknown bacteria were S. epidermidis and E. coli.
We know this because:
-On the TSA plate, there were two types of colonies. We did not know what they were, since it was just a rich medium plate.
-On the MSA plate, there was pink growth, which indicated S. epidermidis.
-On the EMB plate, there was green growth, which indicated E. coli. q
What is the difference between TSA and NA?
They are different but are both rich media
Complete the following:
MSA selects against ____ and selects for the growth of ____.
MSA selects against all other bacteria and selects for the growth of halotolerant bacteria.
Complete the following:
MSA differentiates between ___ and ___, based on the ability to ferment ___ to acid.
MSA differentiates between mannitol fermenters (which are yellow) and non-mannitol fermenters (which are pink), based on the ability to ferment mannitol to acid.
Complete the following:
EMB selects against ___ and selects for the growth of ____.
EMB selects against Gram-positive and selects for the growth of Gram-negative.
Complete the following:
EMB differentiates between __, __, and ___, based on the ability to ferment ___ and/or ___ to acid.
EMB differentiates between:
1. Non-fermenters (clear)
2. Slow-fermenters (pink)
and
3. Fast-fermenters (metallic green)
Based on the ability to ferment sucrose and/or lactose into acid.
What happens in EMB plates is there is no sucrose or lactose to ferment?
It will ferment peptides and amino acids.
